I would offer that PLD is actually quite a topic—it certainly was when I was still serving—and it has to do with the disparities in the costs of living among different parts of the country. Some have far better access to housing, as you can imagine, than others do. In certain areas, specifically those areas that are hard to reach—Cold Lake comes to mind—housing is very expensive, so this post living differential is supposed to help create equality among armed forces members across the country.
The issue, in my humble opinion, is that there is just not enough PLD to go around to sufficiently address all of the people in the Canadian Armed Forces who live in areas in which the housing market is so expensive. I don't think it is sufficient.